Last week may have marked when the last piece was put in place for all-electric cars to become a common reality. At an event in Los Angeles, electric car pioneer Tesla showed how it could hot-swap batteries in its Model S. In fact, it swapped batteries twice in the time it took to fill up a conventional car.

In the demonstration, the gas tank of an Audi A8 was filled with 28 gallons of gas, while an automated swapped two, fully charged batteries into two Tesla Model S vehicles, first one and then the other. The Model S's range for a single battery is over 200 miles.

The Tesla employee filling the Audi was shown doing so via an unedited video shot at a gas station in Los Angeles, and the company said that it had made attempts to find the fastest-filling pump. The battery swapping was conducted before a live crowd Thursday night at Tesla's design center.

1,000-Pound Battery

The battery swap currently is a process specific to Tesla. The large, flat, 1,000-pound battery pack resides under the floor of the car and, in fact, helps support the chassis. To change it, the Model S drives into a pit not unlike one used to perform an oil change. A robotic device below the car removes the bolts, removes the pack and then installs and bolts in a fresh one.

Tesla has announced it will begin installing its hot-swap stations in the next few years, accompanying its Supercharger stations. Supercharger stations can fast-charge the Model S batteries to half-full in half an hour or less, and Tesla does not charge for the electricity, so the Supercharging is free. A Supercharge delivers about 160 miles of electricity into the batteries.

Tripling Superchargers

In May, Tesla announced it will increase the number of its Supercharger stations from eight to 27 by the middle of this summer, and by 2015 it will have enough Supercharger locations so that a Tesla owner could drive across the U.S. Consumer Reports magazine said it would have awarded the Model S a perfect score in its review, except for the fact that one can't drive anywhere for any length of time.

Currently, Superchargers are located along three main travel routes -- between San Francisco and Los Angeles, Los Angeles and Las Vegas, and Boston and Washington, D.C.

CEO Elon Musk has indicated that the company will charge under $100 for a Model S battery swap, which is about the same as the cost of filling up the Audi A8's tank. The battery-swap machine runs about a half-million dollars, and must be installed into a pit of proper size. Musk said owners of the Model S will be automatically billed as their car enters the changing station, and the occupants could remain in the car during the process if they wish.

Since the Supercharger charging is free while the battery swap is not, Musk said the Model S driver will simply need to decide if they prefer "free or fast."